A typical light fixture for a bipin-base fluorescent lamp has a pair of lamp holders between which the lamp fits. Each holder has a housing with a mouth and a rotor rotatably supported in the housing adjacent the mouth and having an installation slot for receiving contact pins of the fluorescent lamp and, when the mouth is brought into alignment, for defining a lamp installation position. The rotor guides the lamp pins when the lamp is rotated in the holder along a circular orbit into a contact position for making contact with holder contacts supported in the housing. The rotor assumes in the contact position an engagement position that at least partially impedes rotation.
Lamp holders of the above-described type usually serve for the electrical connection of fluorescent lamps with a socket on both ends—especially fluorescent tubes with G13 sockets—that comprise two lamp pins on their holder side and extend parallel to the longitudinal axis of the lamp. The housing as well as the rotor each have a mouth and an installation slot that, when brought into alignment, make it possible to install the lamp in the holder. In the installed state the lamp pins are recessed in the rotor.
For making electrical contact with holder contacts provided in the housing and usually designed as spring contacts, the lamp is rotated to entrain the rotor, during which a 90° rotation is usually required in order to reach the contact position.
In order to make the contact position recognizable for the user and to ensure that the lamp remains in this contact position, the rotor comprises at least one engagement position. German Utility Model 1 915 204 discloses for example an engagement plate provided underneath the rotor whose engagement cams directed to the rotor engage recesses on the rotor. GB 591676, on the other hand, shows a spring contact opened in an approximate V-shape toward the rotor center and in which the lamp pins are gripped after the rotor has been rotated through 90°—starting from the installation position. JP 2002-100450 shows a similar solution for making the contact position recognizable.
Further generic publications showing corresponding holders with at least one contact position made recognizable by engagement or catching are, e.g. CH 266505, GB 581097 or German Utility Model 6914559. Holders with intermediate engagement positions are also known from the prior art.
Even if the possibilities for making the contact position of the fluorescent lamp in the holder recognizable consistently fulfill its function, a plurality of which are known from the state of the art, they have disadvantages.
The lamp replacement is not only carried out by trained personnel but usually by users that are not informed in detail about the technical design of such a lamp holder. Since fluorescent lamps become at least moderately warm in operation and illumination systems can frequently not be completely turned off, the replacement of a defective lamp frequently takes place under applied voltage. As a consequence, the replacement lamp lights up as soon as the lamp pins contact the holder contacts for the first time. In the case of the prior-art holders the contact between lamp pins and holder contacts usually takes place far before reaching the contact position in which a reliable seating of the lamp in the holder and a contact, e.g. with good contact pressure between the contacts on the holder and the contact pins on the socket, are assured. Due to a lack of is knowledge of the user, the fluorescent lamps remain loose since lighting of the lamp allows an orderly function to be assumed.
However, it has turned out that an orderly function is not given in a loose position. Vibrations, jolts or changes in position of the lamp pins due to temperature fluctuations can result in the fluorescent lamp and the non-engaged rotor readily moving, so that contact between the lamp and the holder is intermittently or completely interrupted. As a result, the lamps are considered to be faulty or defective or an unpleasant flickering occurs due to uncontrolled intermittent contact and the associated repetitive ignitions of the lamp, which for its part strains the so-called starter of the lamp and/or the operating apparatus and results in premature aging. Even damage to the holder contacts and/or lamp pins by arcing is possible. In a few cases the misaligned rotor can also rotate again into its installation position so that the installation slot of the housing and of the rotor are then in alignment. In the worst case the lamp then becomes detached from the holder and falls out.